GEC, BHAVNAGAR DEPT.
OF ICT
EXPERIMENT NO-2 DATE:
AMPLITUDE MODULATION &DEMODULATION
AIM: (i) To study the function of Amplitude Modulation & Demodulation (under
modulation, perfect modulation & over modulation) and also to calculate the modulation
index.
(ii) To verify the spectrum of AM signals using spectrum analyzer.
APPARATUS :
1. Amplitude Modulation & De modulation trainer kit.
2. C.R.O (20MHz)
3. Function generator (1MHz).
4. Connecting cords & probes.
5. PC with windows(95/98/XP/NT/2000)
6. MATLAB Software with communication toolbox
THEORY:
Modulation is defined as the process of changing the characteristics (Amplitude,
Frequency or Phase) of the carrier signal (high frequency signal) in accordance with the
intensity of the message signal (modulating signal).
Amplitude modulation is defined as a system of modulation in which the amplitude of
the carrier is varied in accordance with amplitude of the message signal (modulating signal).
The message signal is given by the expression.
Em(t) =Em cosWmt
Where Wm is------> Angular frequency
Em-------- Amplitude
Carrier voltage Ec(t)= Ec cosWct
E(t)=Ec + KaEm cosWmt
KaEm cosWmt----- change in carrier amplitude
Ka----- constant
The amplitude modulated voltage is given by
E=E(t) cosWct
From above two equations
E= ( Ec+KaEm cosWmt) cosWct.
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GEC, BHAVNAGAR DEPT.OF ICT
E= (1+KaEm/Ec cosWmt) Ec cosWct
E= Ec(1+Ma cosWmt)cosWct
Where Ma----- depth of modulation/ modulation index/modulation factor
Ma=KaEm/Ec
100* Ma gives the percentage of modulation.
BLOCK DIAGRAM:
Modulation
Modulating
Signal
Generator
A.M
modulator
Carrier
Generator
Demodulation
Modulating
Signal AM AM
Generator Modulator Demodulator
Carrier
Generator
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GEC, BHAVNAGAR DEPT.OF ICT
PROCEDURE:-
VLAB- https://kcgcollege.ac.in/Virtual-Lab/Electronics-and-Communication-
Engineering/simulation.html
Amplitude Modulation and Demodulation
Out of the three parameters in any given waveform, ie., amplitude , frequency and
phase, If the amplitude of message is varied with respect to the high frequency
signal(Carrier) the resultant will a modulated signal.
AMPLITUDE MODULATION WAVE FORMS
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GEC, BHAVNAGAR DEPT.OF ICT
Where and are mathematical expression
for modulating and Carrier Signal.
The modulation Index can be Calculated Using the Formulae
Under Modulation
If the depth of modulation is less than 1, then the resulting output is as shown in the figure.
Under Modulated Wave
Over Modulation
If the depth of modulation higher than 1, then the resulting output is as shown in the
figure.
Over modulated Wave
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GEC, BHAVNAGAR DEPT.OF ICT
Output
Conclusion:
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GEC, BHAVNAGAR DEPT.OF ICT
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